Cutting inserts for material machining, in particular for cutting metal machining, comprise a substrate body of carbide, cermet, ceramic. steel or high speed steel which in most cases is provided with a single-layer or multi-layer carbide coating for improving the cutting and/or wearing properties. The carbide coating comprises mutually superposed layers of monometallic or mixed-metallic carbide phases. Examples of monometallic carbide phases are TiN, TiC, TiCN and Al2O3. Examples of mixed-metallic phases in which in a crystal one metal is partially replaced by another are TiAlN and TiAlCN. Coatings of the above-indicated kind are applied by CVD processes (chemical vapour phase deposit). PCVD processes (plasma-assisted CVD processes) or PVD processes (physical vapour phase deposit).
It has been found that certain preferential orientations of crystal growth in the deposit in the PVD or CVD process can have particular advantages, in which respect different preferential orientations of given layers of a coating can also be particularly advantageous for different uses of the cutting insert. The preferential orientation of growth is generally specified in relation to the plane of the crystal lattice defined by way of the Miller index and is referred to as the crystallographic texture (for example fibre texture).
WO 2013/134796 discloses a cutting insert which at least region-wise has a coating formed from one or more coating layers, wherein at least one coating layer includes aluminium, titanium and nitrogen and at least partially has lamellae of a lamella thickness of less than 100 mm, wherein the lamellae include alternate first and second portions with different phases, wherein the first portions predominantly or exclusively comprise hard cubic phase and the second portions predominantly or exclusively comprise soft hexagonal phase. In that case the interplay between the succession of a hard cubic phase and a soft hexagonal phase is intended to promote the strength by virtue of the specific configuration of the structure in the nanometer range, the softer hexagonal component predominating. It is found however that layers with components of hexagonal phase have inadequate wear resistance in particular in the milling or turning machining of steel and cast materials, at high cutting speeds.
WO 2012/126030 discloses a cutting insert having a multi-layer coating which has at least one coating layer with AlxTi1−xN with x≥0.7, wherein the proportion of cubic AlxTi1−xN phase is preferably 70 to 80 mol-% and the remaining proportions are formed by hexagonal AlN and cubic TiN. The proportion of hexagonal AlN is preferably more than 12.5 mol-%. The wear resistance of such coatings is also inadequate by virtue of the proportion of hexagonal AlN. It is assumed that the presence of the three stated phases is based on partial breakdown of the cubic AlxTi1−xN phase into the thermodynamically stable hexagonal AlN and cubic TiN phases and the remaining proportion of cubic AlxTi1−xN phase is not only thermodynamically but also kinetically unstable, which leads to a further breakdown, thereby resulting in mechanical weakening of the layer.
J Keckes et al “Self-organized periodic soft-hard nanolamellae in polycrystalline TiAlN thin films”, Thin Solid Films 545 (2013), pages 29-32, describe polycrystalline Ti0.05Al0.95N layers deposited by means of CVD with periodically alternating cubic TiN and hexagonal AlN nanolamellae within individual crystallites. Kinetically controlled oscillating reactions at the separation surface are proposed as a possible mechanism involved in lamellae formation. The Ti0.05Al0.95N layers were deposited in the MT-CVD process at 800° C. inter alia on carbide substrates. Characterisation of the layers was effected by means of X-ray diffraction (XRD) and conventional and high-resolution transmission electron microscopy (TEM and HR-TEM). The XRD data of the deposited Ti0.05Al0.95N layers showed the presence of both cubic and also hexagonal Ti—Al—N phases. Powder X-ray diffraction analyses of the Ti0.05Al0.95N material and quantitative Rietveld analysis gave proportions by volume of hexagonal AlN (w-AlN), cubic AlN (c-AlN) and cubic TiN (c-TiN) of about 53, 26 and 21%. The hardness of the layer was about 28 GPa. The TEM analysis of cross-sections of the Ti0.05Al0.95N layers on carbide revealed the presence of lamellar periodic structures. By means of HR-TEM and Fourier transform (FFT) it was possible to show that the lamellae have periodically alternating c-TiN and w-AlN, wherein the w-AlN-containing lamellae were about 10 nm in thickness and the c-TiN-containing lamellae were about 3 nm in thickness. With those layers, inadequate wear resistance is also to be encountered because of the high proportion of hexagonal w-AlN phase.
DE 10 2005 032 860 discloses a carbide coating with a layer of face-centred cubic Ti1−xAlxN with an Al content of 0.75<x<0.93 and a process for the production thereof.
DE 10 2007 000 512 discloses a carbide coating with a layer of TiAlN which is deposited on a first layer of TiN. TiCN or TiC deposited directly on the substrate, and a bonding layer provided between the two layers, with a phase gradient. The layer of TiAlN has a preferential orientation of crystal growth with respect to the (200) plane of the crystal lattice.
Laid-open specifications WO 2009/112115, WO 2009/112116 and WO 2009/112117A1 disclose TiAlN and TiAlCN layers deposited by means of CVD processes with a high Al proportion and a face-centred cubic lattice, but no crystallographic preferential orientations of crystal growth are described.
TiAlN coatings produced by means of PVD processes, with various crystallographic preferential orientations of crystal growth, are known, but PVD coatings with face-centred cubic lattices of the TiAlN coatings, in contrast to CVD coatings, are restricted to Al contents of less than 67%. TiAlN coatings with a crystallographic preferential orientation of the {200} plane with respect to the growth direction of the crystallites are described as advantageous for metal machining (for example US 2009/0274899. US 2009/0074521 and WO 2009/127344).